Arrangement in a measuring system

ABSTRACT

System and sensor ( 10 ) for imaging characteristics of an object ( 2 ). The sensor comprises at least a first area ( 11 ) and a second area ( 12 ) of pixel elements arranged to absorb electromagnetic radiation from the object ( 2 ) and to convert the radiation absorbed into electrical charges. The first area ( 11 ) has a first degree of resolution and the second area ( 12 ) has a second degree of resolution different from the first degree of resolution and the first area ( 11 ) is arranged to image one type of characteristics and the second area ( 12 ) is arranged to image another type of characteristics.

TECHNICAL FIELD

The present invention relates in general to a sensor and a system forimaging characteristics of an object and relates in particular to asensor and system for imaging multiple characteristics of an object withdifferent degrees of resolution.

PRIOR ART

Conventional imaging sensors of the charge coupled device (CCD) andcomplementary metal oxide semiconductor (CMOS) type have an N×M matrix(array) with photodiodes, which absorb electromagnetic radiation andconvert this into electrical signals.

There is often a requirement for imaging multiple characteristics of thesame object, such as various three-dimensional (3D) and two-dimensional(2D) characteristics. In the 3D image geometrical characteristics suchas width, height, volume etc. of the object are imaged. In the 2D imagecharacteristics such as cracks, structural orientation, position andidentity are imaged, for example, through marks, bar code or matrixcode. Intensity information in the 2D image is usually imaged in greyscale, but imaging the 2D image in colour, that is to say registering R(red), G (green) and B (blue) components, for example, by means offilters or light wavelengths is also common.

A matrix array picture processor (MAPP sensor) is used for Imagingdifferent characteristics of the same object using the same sensor,so-called multisensing, by using a part of the sensor for laserprofiling (3D measurement) and individual sensor rows for reading outintensity information (2D measurement). An advantage in using one sensorto image multiple characteristics is that the cost and complexity of thesystem are less than when using one sensor for the 3D measurement andanother sensor for the 2D measurement, for example.

In multisensing, the same resolution is nowadays used for lateralmeasurement both in the 2D measurement and in the 3D measurement. It isusual, however, to require a higher resolution on the 2D image than onthe 3D image. The reason for this is the desire to be able to measurefiner detail in the image than is required in measurement of the shape.An example of this is timber inspection, where it is often moreimportant to measure cracks and surface structure with a higherresolution than the geometric shape.

Examples of imaging sensors which have different degrees of resolutionare shown in Alireza Moini “Vision chips”, Kluwer Academic Publishers,page 143-146, 2000, in which image sensors are constructed as anelectronic eye, that is to say they have a high resolution in the centreand a low resolution at the periphery. The pixel geometry in these“eyes” is linear-polar or log-polar. If the “eye” sees somethinginteresting at its periphery with a low resolution, the system cancontrol the sensor so that it directs its high-resolution centre part tothe area in order to read the details. This type of sensor is very wellsuited for robot applications. An example of such an electronic eye isalso shown in U.S. Pat. No. 5,166,511.

Another example of an imaging sensor which has different degrees ofresolution is shown in U.S. Pat. No. 6,320,618, in which an arraymatrix-type sensor has been provided with at least one area having ahigher resolution than the rest of the sensor. The sensor is placed in acamera, which is mounted on a vehicle as a part of an automaticnavigation system, which controls functions of the vehicle, for examplebraking if some obstacle appears in front of the car or steering alongthe white line at the edge of the road. The sensor is arranged to pickup remote information with a high resolution and information inproximity to the vehicle with a low resolution.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a sensor and a systemwhich image the characteristics of an object with different degrees ofresolution. This has been achieved by a sensor and a system having thecharacteristics specified in the characterising parts of claims 1 and 9respectively.

One of the advantages to the use of a sensor and a system which read inmultiple characteristics images with different degrees of resolution isthat a simpler, cheaper and more compact solution is obtained than withpreviously known solutions. A system according to the inventionfurthermore requires fewer system components such as cameras, lensesetc.

According to one embodiment of the present invention the sensorcomprises two integral areas with pixels which are arrangedsubstantially parallel, side by side in a transverse direction.

According to another embodiment of the invention the two areas withpixels are designed as two separate units, which are arrangedsubstantially parallel, side by side in a transverse direction

According to a further embodiment of the invention the two pixelareas/units share read-out logic, which means that they have the sameoutput register.

According to an alternative embodiment of the invention the two pixelareas/units are each read out on different output registers, which meansthat it is possible to read out the information contained in the twoareas/units simultaneously. One advantage to this is that it obtainsgreater freedom with regard to exposure times. Another advantage is thatit obtains greater freedom with regard to degrees of resolution in boththe transverse direction and the lateral direction.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained in more detail on the basis ofexamples of embodiments and with reference to the drawings attached inwhich:

FIG. 1 shows a perspective view of a measuring system according to thepresent invention;

FIG. 2 shows a three-dimensional profile and intensity profile of anobject imaged on the sensor;

FIG. 3 shows a first embodiment of a sensor according to the invention;

FIG. 4 shows a second embodiment of a sensor according to the invention;

FIG. 5 shows an alternative embodiment of a sensor according to theinvention;

FIG. 6 illustrates a fundamental system setup according to a firstembodiment;

FIG. 7 illustrates a fundamental system setup according to a secondembodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows a system for reading in characteristics of an object. Thesystem comprises a camera 1, which may be an MAPP camera, a CCD camera,a CMOS camera or any other camera suitable for imaging characteristicsof an object. The system further comprises an object 2, thecharacteristic-dependent parameters of which are to be measured by thesystem, placed on a base 3 together with two light sources 4 and 5arranged to illuminate the object 2. The light sources 4, 5 generate,for example, substantially point light, substantially linear light orlight composed of multiple, substantially point or linear segments andmay be of any type suited to the application, for example lasers, LED's,ordinary light (light bulb) etc, but these are familiar to the personskilled in the art and will not be further described here.

The camera 1 comprises, among other things, a sensor 10, which is shownin FIGS. 2 to 5 and is described in more detail below, light-gatheringoptics and control logic (not shown). The rays reflected from the object2 are picked up by the sensor 10 and are converted there into electricalcharges, which are in turn converted into analog or digital electricalsignals. In the preferred embodiment these signals are then transferredvia an output register (shown in FIGS. 6 and 7) to animage/signal-processing unit (not shown) to be analysed and processed.

The object 2, which as stated above, has been placed on the base 3,which in a preferred embodiment moves relative to the measuring systemindicated by an arrow in the figure. Instead of the base 3 movingrelative to the measuring system, the relationship may naturally bereversed, that is to say the object 3 is fixed and the measuring systemmoves over the object 2 when measuring. The base 3 may be a conveyorbelt, for example, or alternatively there is no base and the objectitself moves, if the said object is paper, for example, in a continuousweb in a paper-making machine.

In an alternative embodiment (not shown), one or more of the lightsources is located below the base 3 and shines through the object 2,which means that the sensor 10 picks up transmitted rays which havepassed through the object 2, and not reflected rays.

In FIG. 1 the direction of movement is indicated by an arrow. Thisdirection will be referred to in this document as the transversedirection, that is to say Y in the system of coordinates drawn into thefigure. The lateral direction (X in the system of coordinates) liesperpendicular to the transverse direction. In measuring there is atransverse and a lateral resolution. The transverse resolution dependson how frequently the object 2 is read off (sampled). The presentinvention is primarily concerned with the lateral resolution, whichlargely depends on the number of pixels which the sensor 10 has in arow.

The sensor 10 (shown in FIGS. 2 to 5) is an array sensor and has a firstarea 11 with N×M pixels (where N is rows and M is columns) combined witha second high-resolution area 12 with X×Y pixels, where Y=M×b (b is aninteger >1). In the preferred embodiment the first area 11 is used for3D measurement by tri-angulation, that is to say imaged geometriccharacteristics of the object 2 such as width, height, volume etc. In 3Dmeasurement, the intensity image is reduced from k rows, k>1, to theposition values that correspond to where the light strikes the sensor ineach column. The result is a profile with three-dimensional informationfor each sample of k rows. In the preferred embodiment the second area12 is used for 2D measurement (intensity information), that is to say inimaged characteristics of the object 2 such as cracks, structuralorientation, position etc. If X>2, there is a possibility of applyingcolour filters (for example, RGB) to the individual pixels and in thisway obtaining a colour read-out of 2D data.

FIG. 2 shows a 3D profile of the object 2 in the first area 11 and agrey scale/colour image of the object 2 in the second area 12. Theobject 2 is scanned profile by profile as the object 2 passes themeasuring system and the result is accordingly a three-dimensional and atwo-dimensional imaging of the object 2.

In the preferred embodiment an MAPP sensor is used, but the personskilled in the art will appreciate that the invention may be applied toother types of sensors, such as CCD sensors or CMOS sensors, forexample.

FIG. 3 shows a first embodiment of the sensor according to theinvention. Here the pixels in the second area 12 are one third the widthof the pixels in the first area 11. If there are 512×1536 pixels in thefirst area 11, for example, the second area 12 then has 16×4608 pixels(b=3), for example. This means that up to 512 rows are used for the 3Dmeasurement and triple resolution intensity components are read out onup to 16 rows.

In the embodiment according to FIG. 4 every other row in the secondhigh-resolution area 12 is offset half a pixel width in relation to therows immediately below and above. The second area 12, according to theexample for FIG. 3, then has 8×3072 double rows of pixels (b=2), inwhich a double row consists of two single rows and one row is offset byhalf a pixel width. This means that in the embodiment according to FIG.4 up to 512 rows are used for 3D measurement and up to 8 differentdouble-resolution intensity components are read out.

The person skilled in the art will appreciate that the invention is notlimited to the embodiments shown in FIGS. 3 and 4. There is an almostinfinite number of variants of how the pixels can be formed in thehigh-resolution second area 12. For example, the pixels may be half thewidth of those in the first area 11, or also at the same time twice ashigh etc. Other variants of the embodiment according to FIG. 4 mayinvolve the pixels being offset by a third or a quarter of the pixelwidth. With regard to this, see also U.S. Pat. No. 4,204,230, whichshows offset pixel rows for increasing the resolution of an imagingsensor.

According to FIGS. 3 and 4 the first area 11 and the second area 12 liesubstantially parallel side by side in direct contact in a transversedirection, that it to say the sensor is manufactured as an integralunit. FIG. 5 shows an alternative embodiment in which the first area 11and the second area 12 are two separate units lying substantiallyparallel side by side in the transverse direction, but not in directcontact. In FIGS. 2 to 5 the second high-resolution area 12 is locatedtransversely in front of the first area 11 (illustrated at the top ofthe figures), but naturally it may equally well be located transverselybehind the first area 11 (illustrated at the bottom of the figures).

An alternative to designing the pixels offset in relation to one anotheris to cover the pixels with masks, which are arranged in such a way thatillumination of parts of pixels is blocked and an offset samplingpattern is thereby obtained.

A sensor row is read out to an output register, which is M pixels long,shown in FIGS. 6 and 7. This output register 15, 18 a, 18 b is eitherexchanged as raw data or it is coupled to a row-parallel A/D converterand/or signal/image processing unit. In order to read out a Y-wide row,w read-outs must be performed successively. If the output register 15,18 a, 18 b has space for b rows, these can be read out/processedtogether. The read-out can therefore be both analog and digital, but inthe preferred embodiment of the present invention (shown in FIG. 6),measured data is read out via an A/D converter 16 and a processor 17 toa digital output register 15, before being relayed to animage-processing unit 5 (not shown).

The processor 17 can be programmed to perform many functions, amongother things extracting the three-dimensional profile from the intensityimage, that is to say each column calculates the position of thelightest point and these values can then be seen as an intensity profilein which the intensity corresponds to distance. Other functionsperformed by the processor 17 are edge detection, noise reduction etc.

In an alternative embodiment of the invention, shown in FIG. 7, the twosensor areas 11, 12 (N×M and X×Y) do not share the read-out logic, thatis to say they have different output registers 18 a and 18 b, whichmeans that other effects are obtained. Information from the two areas11, 12 can be read out independently of one another with greater freedomof exposure times and degrees of resolution both in the transverse andin the lateral direction. Furthermore, Y=M×b need not apply, it beinginstead possible to configure the geometries differently, for example a1536×512 matrix could be combined with a 4096×3 matrix. In a preferredembodiment of the alternative embodiment shown in FIG. 7, measured dataare read out via A/D converters 19 a, 19 b and processors 20 a, 20 b todigital output registers 18 a, 18 b.

Both of the embodiments according to FIGS. 6 and 7 are illustrated withA/D converters and processors. These should only be regarded aspreferred embodiments. It is quite possible, as briefly mentioned above,to output measured data directly as analog or digital raw data from theoutput registers.

As stated above, it is possible to use colour filters or coloured lightsources (not shown) on the second area 12 of the sensor 10, which meansthat both grey scale and colour images can be read out with the higherresolution. Which colour filters or coloured light sources are used andhow these are placed will be known to the person skilled in the art andwill not be described in detail here, but the possible use of Bayerpatterns or a filter for each row may be mentioned by way of example.RGB components are commonly chosen, but other colours such as CMY (cyanmagenta yellow) may also be used. In the alternative embodimentaccording to FIG. 7, each colour might have its own output register,which gives a faster read-out of each colour profile.

Crosstalk means that light from one measurement interferes with anothersensor area, that is to say light from the 3D measurement interfereswith the 2D measurement and/or vice-versa. In order to reduce thecrosstalk between different sensor areas it is possible to separate thelight to these into different wavelengths and to protect differentsensor areas with optical filters differing according to wavelength,which block the light or allow it to pass through to the respectivesensor area.

In yet another embodiment of the sensor 1 according to the inventiontime delay integration (TDI) is used on the high-resolution second area12. TDI means that the charge is moved from one row to another as theobject 2 is moved with the base 3, thereby achieving an X-times greaterlight sensitivity with X TDI stages. By using TDI in the embodimentaccording to FIG. 4, the charge will be moved by two rows per stagesince intervening rows are offset by half the pixel width.

1. A sensor, comprising at least a first area and a second area of pixelelements arranged to absorb electromagnetic radiation from an object,the characteristics of which are to be imaged, and to convert theradiation absorbed into electrical charges, in which the first area hasa first degree of resolution and the second area has a second degree ofresolution different from the first degree of resolution, the first areais arranged to image one type of characteristics and the second area isarranged to image another type of characteristics.
 2. The sensoraccording to claim 1, wherein the first area is arranged to imagethree-dimensional characteristics of the object and that the second areais arranged to image two-dimensional characteristics of the object. 3.The sensor according to claim 1, wherein at least one of the two areasis provided in its entirety or partially with color filters in order toimage the object in color.
 4. The sensor according to claim 1, whereinthe first area is designed as a matrix having N rows and M columns, thatthe second area is designed as a matrix having X rows and Y columns andthat Y is b multiplied by M columns, where b is an integer greater thanzero.
 5. The sensor according to claim 4, wherein time delay integrationis used on the second area.
 6. The sensor according to claim 1, whereinat least one of the areas is provided with filters for differentwavelengths in order to minimize crosstalk.
 7. The sensor according toclaim 1, wherein the first area and the second area are arrangedparallel in a transverse direction as one integral unit.
 8. The sensoraccording to claim 1, wherein the first area and the second area arearranged parallel in a transverse direction as two separate units.
 9. Asystem for measuring character-dependent parameters of an objectcomprising at least one light source which emits light towards theobject, wherein the system further comprises a sensor according to claim1, arranged to absorb electro-magnetic radiation from the object and toconvert it into electrical charges.
 10. The system according to claim 9,wherein the system also comprises an output register arranged to readout the charges received in the sensor.
 11. The system according toclaim 9, wherein the system also comprises at least two output registersarranged to read out the charges received in the sensor.
 12. The sensoraccording to claim 11, wherein the first area and the second area of thesensor are each read out on their own output register.
 13. The sensoraccording to claim 11, wherein if the second area of the sensor isprovided with color filters, color picked up has its own outputregister.
 14. The system according to claim 10, wherein the systemfurther comprises an A/D converter arranged to convert the electricalcharges from an analog to a digital format and that the output registeris a digital output register.
 15. The system according to claim 9,wherein the system also comprises an image/signal processing unitarranged to alanyze the electrical charges.